The Akkadian Empire was the first united empire in Mesopotamia and was established at 4.6 kyr B.P. (where present is A.D. 1950). The empire abruptly collapsed in 4.2 ± 0.2 kyr B.P. Seasonal-scale climatic dynamics behind this collapse have not yet been resolved. Here, we present monthly climatic parameters (temperature and hydrology) inferred from fossil Omani corals that lived between 4.5 and 2.9 kyr B.P. Winter temperatures derived from a modern Omani coral correlate with winter shamal (western Asian dust storm) frequency. A fossil coral from 4.1 kyr B.P. shows a prolonged winter shamal season with frequent shamal days. This likely caused agricultural failures in Mesopotamia and contributed to the Akkadian Empire collapse, as this region depends on winter rainfall. INTRODUCTION Mesopotamian civilizations thrived following the development of irrigation and rain-fed agriculture between the Euphrates and Tigris Rivers (Jacobsen and Adams, 1958; Wilkinson et al., 1994; Macklin and Lewin, 2015) (Fig. 1A). The first united empire in the Mesopotamian region, the Akkadian Empire, was established around the metropolis Tell-Leilan under the rule of Sargon of Akkad in ca. 4.6 kyr B.P. (where present is A.D. 1950) (Weiss et al., 1993; Ristvet and Weiss, 2005). The Akkadian Empire linked the remote rain-fed agricultural lands of northern Mesopotamia with the irrigation-based southern Mesopotamian city-states. Archaeological ruins dated by radiocarbon isotopes show that the Akkadian Empire abruptly collapsed at ca. 4.2 kyr B.P., and its settlements were abandoned (Weiss et al., 1993, 2012; Ristvet and Weiss, 2005). Three-hundred (300) years after the collapse, new populations resettled in the region of the former Akkadian Empire. Soil morphological investigations at TellLeilan suggest a sudden shift toward drier, more arid conditions at ca. 4.2 kyr B.P. (Weiss et al., 1993), while a sediment core from the Gulf of Oman, taken directly downwind of the Akkadian Empire, shows an abrupt increase in aeolian dust from the Mesopotamian region (Cullen et al., 2000). Taken together, these results suggest that the collapse of the Akkadian Empire was caused by an abrupt drought (Weiss, 2017), which involved strong surface winds blowing from western Asia toward the Gulf of Oman– Arabian Sea. However, the climatic processes behind the 4.2 kyr B.P. event still need to be resolved (Staubwasser et al., 2003; Walker et al., 2012; Kathayat et al., 2017). The agriculture of the Akkadian Empire depended on winter rainfall in the headwaters of the Euphrates and Tigris Rivers and on their seasonally varying river discharge (Fig. 1; Macklin and Lewin, 2015). To better constrain the climatic processes that caused the abrupt aridification at 4.2 kyr B.P. in the Mesopotamian basin and the collapse of the Akkadian Empire, paleoclimate reconstructions are required (deMenocal, 2001). Here we reconstruct wintertime temperatures and hydrological changes from six fossil Porites corals sampled in the Gulf of Oman. The fossil corals are from 4.5 to 2.9 kyr B.P.; i.e., they provide time windows of seasonal climate variations before, during, and after the collapse of the Akkadian Empire. MATERIALS AND METHOD We collected fossil Porites colonies from coastal tsunami deposits on the northeastern coast of Oman (city of Fins: 22°54.08′N, 59°13.37′E; Hoffmann et al., 2013; Fig. 1). The coral samples were sliced into 5-mm-thick slabs, which were X-rayed (Fig. DR1 in the GSA Data Repository1). We collected powder samples for geochemical analysis along the maximum growth axes of the corals at 0.2–0.9 mm intervals (Table DR1 in the Data Repository). All fossil corals were screened for diagenetic alteration using scanning electron microscope images and X-ray diffraction analysis (Fig. DR2; Table DR1). For geochemical analysis, we selected fossil corals that did not show any signs of diagenetic alteration. The ages of fossil corals were determined using a radiocarbon technique at the Accelerated Mass Spectrometry Center of Yamagata University (Yamagata, Japan). Ages were corrected for a local reservoir effect following Cullen et al. (2000) and then calibrated using the Marine13 program (Reimer et al., 2013; Table DR2). We used six fossil Porites corals from 4.5 to 2.9 kyr B.P., bracketing the

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阿曼珊瑚表明，更强烈的冬季沙马尔季节导致阿卡德帝国（美索不达米亚）崩溃

阿卡德帝国是美索不达米亚的第一个统一帝国，成立于公元前 4.6 基尔（现在是公元 1950 年）。帝国在 4.2 ± 0.2 kyr BP 中突然崩溃 此次崩溃背后的季节性气候动态尚未得到解决。在这里，我们展示了从生活在 4.5 到 2.9 kyr BP 之间的化石阿曼珊瑚推断出的每月气候参数（温度和水文）。来自现代阿曼珊瑚的冬季温度与冬季沙马尔（西亚沙尘暴）频率相关。来自 4.1 kyr BP 的化石珊瑚显示了漫长的冬季 shamal 季节和频繁的 shamal 日。这可能导致美索不达米亚的农业失败，并导致阿卡德帝国崩溃，因为该地区依赖冬季降雨。引言 随着幼发拉底河和底格里斯河之间灌溉和雨养农业的发展，美索不达米亚文明蓬勃发展（Jacobsen 和 Adams，1958 年；Wilkinson 等人，1994 年；Macklin 和 Lewin，2015 年）（图 1A）。美索不达米亚地区的第一个联合帝国——阿卡德帝国，是在约 10 年的阿卡德的萨尔贡 (Sargon of Akkad) 的统治下，围绕大都会泰莱兰 (Tell-Leilan) 建立的。4.6 kyr BP（现在是公元 1950 年）（Weiss 等人，1993 年；Ristvet 和 Weiss，2005 年）。阿卡德帝国将美索不达米亚北部偏远的雨水灌溉农田与以灌溉为基础的美索不达米亚南部城邦联系在一起。用放射性碳同位素确定年代的考古遗址表明，阿卡德帝国在大约 10 年突然崩溃。4.2 kyr BP，其定居点被废弃（Weiss 等人，1993 年，2012 年；Ristvet 和 Weiss，2005 年）。崩溃后三百 (300) 年，新的人口重新定居在前阿卡德帝国地区。TellLeilan 的土壤形态调查表明，大约在 2000 年，土壤突然转向更干燥、更干旱的环境。4.2 kyr BP (Weiss et al., 1993)，而来自阿曼湾的沉积岩心，直接取自阿卡德帝国的下风向，显示来自美索不达米亚地区的风尘突然增加(Cullen et al., 2000)。综上所述，这些结果表明，阿卡德帝国的崩溃是由突然的干旱引起的（Weiss，2017 年），其中包括从西亚吹向阿曼湾 - 阿拉伯海的强烈地表风。然而，4.2 kyr BP 事件背后的气候过程仍然需要解决（Staubwasser 等人，2003 年；Walker 等人，2012 年；Kathayat 等人，2017 年）。阿卡德帝国的农业依赖于幼发拉底河和底格里斯河源头的冬季降雨及其季节性变化的河流流量（图 1；Macklin 和 Lewin，2015 年）。为了更好地限制导致美索不达米亚盆地 4.2 kyr BP 突然干旱和阿卡德帝国崩溃的气候过程，需要进行古气候重建（deMenocal，2001）。在这里，我们从在阿曼湾采样的六种化石珊瑚礁重建了冬季温度和水文变化。化石珊瑚从 4.5 到 2.9 kyr BP；即，它们提供了阿卡德帝国崩溃之前、期间和之后季节性气候变化的时间窗口。材料与方法 我们从阿曼东北海岸（芬斯市：22°54.08'N，59°13.37'E；Hoffmann 等人，2013；图 1）的沿海海啸沉积物中收集了化石 Porites 群落。珊瑚样本被切成 5 毫米厚的平板，然后进行 X 射线照射（GSA 数据存储库中的图 DR1）。我们沿珊瑚的最大生长轴以 0.2-0.9 毫米的间隔收集粉末样品进行地球化学分析（数据存储库中的表 DR1）。使用扫描电子显微镜图像和 X 射线衍射分析筛选所有化石珊瑚的成岩作用（图 DR2；表 DR1）。对于地球化学分析，我们选择了没有显示任何成岩改变迹象的化石珊瑚。化石珊瑚的年龄是在山形大学（日本山形县）的加速质谱中心使用放射性碳技术确定的。年龄根据 Cullen 等人的局部水库效应进行了校正。(2000)，然后使用 Marine13 程序进行校准（Reimer 等，2013；表 DR2）。我们使用了从 4.5 到 2.9 kyr BP 的六个化石 Porites 珊瑚，将